Single ply membrane roofing systems using EPDM rubber, polyvinylchloride (PVC), and other synthetic material single layer sheets as the top layer of water impervious material were introduced on a large scale to the roofing industry several years ago. The single ply membrane roofing systems are especially advantageous for flat or low pitch roofs, such as are found in most large commercial buildings such as office buildings, shopping centers and the like. The use of such single ply membranes is increasing due to inherent advantages of same over older systems, such as built up roofs formed of layers of tar and paper material (BUR), because of weathering and the lower roof loading weights and the savings in costs for an installed roof.
Since the introduction of such single ply roofing systems on a large scale, there have evolved many different methods of attaching these sheets in position on the roofs. The loose-laid and balasted systems involve the placement of a very large sheet of the membrane over the roof surface and applying gravel on top to hold the same down on the top layer of roof insulation boards.There are also many mechanical fastening systems which clamp the membrane to the roof supporting structure. Known non-penetrating systems which stress clamp the membrane will cause a premature breakdown of the roof membrane in the clamped, stressed area. Other mechanical fastening systems have compression holding devices on top of the membrane and fixed to the building structure by means of a fastener that penetrates from above through the membrane. These "penetrating" fastener systems require some type of path or seal at each penetration, a requirement which leads to installation problems and reliability problems since it is very hard to assure that each and every one of up to several hundred penetrations in a roof are in fact adequately sealed. Wind uplift stress and membrane fluttering with such systems can result in roof failures.
The present invention relates to non-penetrating and non-stress clamping systems and improvements thereof. There have been several known non-penetrating systems. A system which has enjoyed substantial commercial acceptance for use with EPDM rubber sheets is the plate bonded system which has been actively marketed by Kelly Energy Systems Inc. of Waterbury, Connecticut. This plate bonded system is also the subject of applicant's U.S. Patent 4,162,597. This system utilizes relatively rigid masonite or the like pads, each approximately one foot square and made a quarter inch thick, which pads are held on the top of the roof insulation boards by a roof fastener, including a roof washer. The top of these plate bonding pads are then covered by an adhesive and the large EPDM sheets are rolled thereover and adhered thereto. This system exhibits very advantageous wind uplift response characteristics, due to the flexing of the relatively rigid pads and the transfer of forces from expanding air pressure to adjacent areas of the roof via the "balloon" formed because of the elastic nature of EPDM rubber sheet material.
For reinforced and non-ballooning membranes that are relatively inelastic, such as the thermoplastic PVC, Hypalon and copolymer alloy (CPA) membranes and other reinforced membranes, the plate bonded system has not been commercially adapted. Rather, various attachment systems have been used which rely upon the chemical characteristics of the PVC material to hold the same down in the roof installation. One such system is the Trocal (trademark) system developed by Dynamit Nobel AG Company of Germany, which system has been sold commercially in the United States for some years. For attaching the membrane, PVC coated washers are provided to hold down the roof insulation boards. These washers are then heat or solvent welded to the underside of the PVC roofing membrane to hold the membrane down. U.S. Patent 4,161,854 discloses certain features of this system.
Another known PVC membrane attaching system has been marketed by the company, Braas & Co. GmbH of Frankfurt, Germany. This system includes use of a circular piece of the PVC membrane material which is fastened by the roof fasteners in position at the top of the insulation boards. The pieces of PVC membrane material serve as a surface for applying adhesive so that they can be attached to the underside of the PVC roofing membrane. Braas Bulletin 1106, bearing identification number FOKB 1,500 4/77, discloses details of this system. The above-described Trocal and Braas systems have not been adapted for use with EPDM rubber membrane systems, apparently because of the much different characteristics of the unreinforced EPDM rubbers capable of substantial ballooning movement, and reinforced or relatively rigid thermoplastic PVC, Hyplon or CPA materials as regards their elasticity. Also the Trocal PVC system requires that the material at the coating of the washer be compatible with the overlying membrane to facilitate solvent or heat welding attachment.
These prior art systems for PVC membranes require a very large number of fasteners per unit area of the roof in order to meet the wind uplift test conditions that must be met in order to obtain certification for use in certain building applications. Underwriters Laboratory, Factual Mutual and Metro Dade (Florida) are three testing facilities that have established wind uplift and other tests for roofing systems. These systems usually require one fastener per 2-4 ft.sup.2 of roof to acquire a 90 pounds per square foot (PSF) wind uplift rating. These and higher wind uplift ratings may be required for very tall buildings which experience high wind characteristics and wherein the wind uplift conditions are quite severe. Also, different geographic areas have different prevailing wind conditions, consequently resulting in different types of wind uplift resistance standards for different areas.
An object of the present invention is to provide a single ply membrane securing system and method of using same, which overcomes the problems of the prior art in so far as ease of installation, reliability of the finished roofing installations, the tolerance of the roofing installation to wind uplift conditions, and the total costs of the assembled roofs.
These and other objects of the present invention are achieved by providing a roofing membrane securing system which includes membrane securing units formed of flexible sheet material which exhibits an upwardly facing surface which can be adhered securely to the underside of the roofing membrane to hold it in position on a roof, wherein the membrane securing unit exhibits varying thickness across its area. Due to the varying thickness across the area of the flexible membrane securing unit advantages are achieved in adapting to roof fastener systems and in obtaining optimum response to wind uplift conditions due to transfer and sharing of forces on the membrane by adjacent securing units. Further advantages are obtained with respect to ease of assembly and total costs of installation of a roof.
Certain objects of the invention are advantageously achieved when the securing units of the invention are installed in a pre-determined manner with respect to the geometry of the sheets of material being attached. By positioning the securing units along the seams of the overlapping roofing membrane sheets, optimum reinforcement at the seams and at the securing points to the securing units is obtained. According to certain preferred embodiments, the securing units are placed in a geometric pattern over the field of the roof so as to form a "geodesic" dome like force transfer effect for transferring wind uplift forces through the membrane from each securing unit to respective adjacent securing units. Applicant believes that this configuration contributes to the very good wind uplift response characteristics that have been experienced during testing of prototypes of the present invention. In preliminary tests of experimental prototypes of the present invention, a 90 PSF wind uplift rating was obtained with only one fastener per 36 ft.sup.2.
Especially preferred embodiments of the invention are designed for use for reinforced thermoplastic, Hypolan, CPA and PVC single ply membranes system or other relatively inelastic membrane system with compatible materials for the membrane and securing units. In especially preferred embodiments, the securing units are formed under factory conditions using two layers of the single ply membrane system to be attached with one of the layers being a piece of membrane that is smaller than the other piece, which smaller piece is then placed on the larger piece in the bottom position. The larger top piece then serves as a welding area for attaching to the overlying membrane. In certain preferred embodiments, the fastening washer which is placed over the top of the securing unit is also coated with material compatible for welding to the membrane. With this embodiment welding of the membrane to the top of the washer also takes place during the seaming and welding to the securing units.
By placing the securing units along the seams of the sheets of membrane being attached, it is accomplished that one can very easily install the membranes in a reliable, repeatable manner and also facilitate the use of available automatic mechanized seam welding equipment for simultaneously forming the welding seam and the securement at the securing units.
Since the preferred embodiments of securing units are to be manufactured under controlled factory conditions, a precise location of the preformed opening for the fastener and precise location and sizing of the material making up the securing unit can be readily accomplished. In certain preferred embodiments, the roofing washer can also be incorporated within or connected to the securing unit under factory conditions with the corresponding assurance and reliability and consistency of manufacturing. This reliability and consistency in manufacturing is important especially in the roofing industry where the on site installation conditions are many times adverse due to weather conditions, unskilled roof installation personnel, varied roof protrusions, and other construction details, leading to otherwise very difficult to maintain installation consistencies.
Another important advantage of the invention is that the geometric location of the securing units, coupled with the construction of the securing units, minimizes the number of fastener screws that are required to hold down the membrane, thus simplifying the roof assembly installation. In most roofing installations of preferred embodiments of the invention, the fasteners used to hold the securing units for the membrane are not required for holding the insulation boards in position underneath. The number and location of fasteners and securing units is determined by the total geometric area of the field of the roof being attached and the width of the sheets being installed. Although additional fasteners may be needed to hold down insulation boards, only a very small number are usually required to hold down each four foot by eight foot insulation board, for example.
In especially preferred arrangements of the present invention, the fasteners and securing units for the membrane are placed at six foot intervals, thus only one fastener is needed for each approximately 36 square feet of the field of the roof, substantially less than prior art arrangements with similar thermoplastic membranes exhibiting similar wind uplift characteristics. In certain preferred embodiments, the securing units are constructed so as to have different strength characteristics in different directions corresponding to the in use positioning of the securing units in a roof installation. The increased strength characteristics are directed along lines corresponding to lines leading to the next adjacent securing units, whereby optimum transfer of forces between their respective securing units is obtained.
In especially simple to construct preferred embodiments, the different directional strength characteristics are obtained by utilizing two square pieces of membrane material welded together and angularly offset with respect to one another so that the corners thereof lie on respective eight radial lines leading from the center of the securing unit in a symmetrical manner.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings(s) which show, for purposes of illustration only, several embodiments in accordance with the present invention.